High-level secretion of biologically active recombinant porcine follicle-stimulating hormone by the methylotrophic yeast Pichia pastoris

Development of Recombinant Follicle-Stimulating Hormone for the Superovulation of Cattle: A Review

Embryo transfer technology is extensively utilized in cattle breeding, with superovulation serving as its foundation. Superovulation currently relies on the administration of exogenous hormones to stimulate follicular development and maturation in the ovaries, with porcine pituitary-derived follicle-stimulating hormone (FSH) being the most commonly used. However, pituitary-derived FSH requires multiple injections, contains luteinizing hormone (LH) and other proteins, and carries a risk of disease transmission. The development of recombinant FSH proteins through protein recombinant technology represents a significant research direction for addressing the aforementioned challenges. Over the past 30 years, extensive studies have been conducted on the development of recombinant bovine, ovine, or porcine FSH. Nevertheless, to date, no commercially recombinant FSH has been widely applied in the superovulation of cattle. This review provides an overview of the molecular design, selection of expression systems, and biological activity of recombinant bovine, ovine, or porcine FSH. This review also summarizes the results of utilizing recombinant FSH in superovulation protocols for cattle. The utilization of recombinant proteins as an alternative to traditionally extracted products in livestock production represents an irreversible trend. The livestock industry is highly sensitive to costs; therefore, it is essential to develop high-quality and cost-effective recombinant FSH products through appropriate molecular design and the use of suitable expression systems.

Development of highly bioactive long-acting recombinant porcine FSH for batch production management of sows

To improve the economic benefits, exogenous hormones are used to control follicular development and synchronize ovulation in the batch flow management of gilts and weaned sows. Equine chorionic gonadotropin (eCG) is widely used to stimulate follicular development in both experimental and farm animals. Despite its effectiveness, several side effects have been found, including the occurrence of follicular cysts, follicular premature luteinization, and increased follicular atresia. As eCG is a heterologous protein, the generation of antibodies has been found in the superovulation of cattle. Moreover, the extraction of eCG from pregnant mare serum raises concerns regarding animal welfare, as well as potential risks for disease transmission. Follicle stimulating hormone (FSH) controls the follicular growth and maturation in the porcine ovary under physiological conditions. In the current study, we developed a novel long-acting recombinant porcine FSH (rpFSH-pFc) consisting of porcine FSH and porcine fragment crystallizable (Fc) via (G4S)3 linker by using the available protein fusion technology to control the follicular development and maturation. The results of pharmacokinetic studies indicated that rpFSH-pFc exhibited a prolonged half-life in both rats and sows. The efficacy of rpFSH-pFc was confirmed by cAMP level evaluation and germinal vesicle breakdown (GVBD) analysis in vitro. Through ovarian weight gain, superovulation and fertility testing assays, our results revealed that a single rpFSH-pFc treatment could effectively promote follicular development and maturation in vivo. Meanwhile, the mRNA expression levels of the target genes associated with follicular development, maturation and ovulation were significantly up-regulated after rpFSH-pFc treatment. Taken together, our results revealed that rpFSH-pFc could bind to the FSH receptor, stimulate follicular growth and development in female mice, and possess a prolonged half-life in both rats and sows. These characteristics suggest that rpFSH-pFc may be an ideal candidate for promoting follicular growth and development in livestock production.

Improving heterologous expression of porcine follicle-stimulating hormone in Pichia pastoris by integrating molecular strategies and culture condition optimization

Porcine follicle-stimulating hormone (pFSH), comprising α and β subunits, is commonly used to induce superovulation in domestic animals in assisted reproduction technologies; however, the practical application of pFSH is inhibited by the limited efficiency of its production. Recombinant yeast-derived FSH offers a practical alternative; however, the heterologous expression efficiency remains disappointingly low. To improve FSH production in Pichia pastoris, a series of molecular strategies, together with fermentation optimization, were tested in the present study. By comparing clones of the Mut^s phenotype strain, it was observed that the yield of soluble pFSH increased by approximately 96% in clones of the Mut⁺ phenotype strain. The protein levels of soluble pFSHβ, which confers biological specificity, increased by approximately 143 and 22% after two kinds of codon optimization strategies, respectively. Moreover, compared with the production of soluble pFSHβ and SUMO-pFSHβ, the production of soluble protein HSA-pFSHβ was significantly improved. Furthermore, the optimum pH and methanol concentration for expressing soluble HSA-pFSH in strain H3-3 were determined as 5.0-6.0 and 1.5-2% in shake-flask, and the yield of soluble HSA-pFSH could reach 40.8 mg/l after purification. In vitro bioactivity assays showed that recombinant HSA-pFSH could efficiently stimulate cAMP synthesis in HEK293 cells expressing porcine FSHR. In conclusion, our results demonstrated that the application of phenotypic selection of aox1 mutants, combined with codon optimization, the choice of fusion partners, and fermentation optimization, considerably increased the yield of pFSH in supernatant of P. pastoris and thus provided a valuable reference for the large-scale recombinant expression of pFSH.

Trends in recombinant protein use in animal production

Recombinant technologies have made possible the production of a broad catalogue of proteins of interest, including those used for animal production. The most widely studied proteins for the animal sector are those with an important role in reproduction, feed efficiency, and health. Nowadays, mammalian cells and fungi are the preferred choice for recombinant production of hormones for reproductive purposes and fibrolytic enzymes to enhance animal performance, respectively. However, the development of low-cost products is a priority, particularly in livestock. The study of cell factories such as yeast and bacteria has notably increased in the last decades to make the new developed reproductive hormones and fibrolytic enzymes a real alternative to the marketed ones. Important efforts have also been invested to developing new recombinant strategies for prevention and therapy, including passive immunization and modulation of the immune system. This offers the possibility to reduce the use of antibiotics by controlling physiological processes and improve the efficacy of preventing infections. Thus, nowadays different recombinant fibrolytic enzymes, hormones, and therapeutic molecules with optimized properties have been successfully produced through cost-effective processes using microbial cell factories. However, despite the important achievements for reducing protein production expenses, alternative strategies to further reduce these costs are still required. In this context, it is necessary to make a giant leap towards the use of novel strategies, such as nanotechnology, that combined with recombinant technology would make recombinant molecules affordable for animal industry.

Cloning and Expression of Iranian Turkmen-thoroughbred Horse Follicle Stimulating Hormone in Pichia pastoris

BACKGROUND

Follicle stimulating hormone (FSH) plays an essential role in reproductive physiology and follicular development.

OBJECTIVE

A new variant of the equine fsh (efsh) gene was cloned, sequenced, and expressed in Pichia pastoris (P. pastoris) GS115 yeast expression system.

MATERIALS AND METHODS

The full-length cDNAs of the efshα and efshβ chains were amplified by reverse transcription polymerase chain reaction (RT-PCR) using the total RNA isolated from an Iranian Turkmen-thoroughbred horse's anterior pituitary gland. The amplified efsh chains were cloned into the pPIC9 vector and transferred into P. pastoris. The secretion of recombined eFSH using P. pastoris expression system was confirmed by Western blotting and immunoprecipitation (IP) methods.

RESULTS

The DNA sequence of the efshβ chain accession number JX861871, predicted two putative differential nucleotide arrays, both of which are located in the 3'UTR. Western blotting showed a molecular mass of 13 and 18 kDa for eFSHα and eFSHβ subunits, respectively. The expression of desired protein was confirmed by protein G immunoprecipitation kit.

CONCLUSIONS

eFSH successfully expressed in P. pastoris. These findings lay a foundation to improve ovulation and embryo recovery rates as well as the efficiency of total embryo-transfer process in mares.

Production of recombinant orange-spotted grouper (Epinephelus coioides) follicle-stimulating hormone (FSH) in single-chain form and dimer form by Pichia pastoris and their biological activities

FSH is a key regulator of steroidogenesis and gonadal growth in teleosts. However, function of FSH is elusive in grouper due to the lack of purified and native FSH. In the present study, we reported production of bioactive orange-spotted grouper (Epinephelus coioides) FSH in dimer form and single-chain form by Pichia pastoris. Dimer form of recombinant grouper FSH (rgFSHba) was accomplished by co-expressing mature FSHb-subunit and a-subunit genes. Fusion of mature FSHb-subunit and a-subunit genes together linking with a polypeptide (4×(Gly-Ser)-Gly-Thr) gene generated single-chain form of recombinant grouper FSH (rgFSHb-a). Recombinant grouper common α-subunit (rgCga) and FSHb-subunit (rgFSHb) were also separately produced. Recombinant proteins were verified by Western blot and mass spectrometry assays, and characterized by deglycosylation analysis. Deglycosylation assay suggested that glycosylation of recombinant FSH mainly occurred on common a-subunit. Bioactivities of recombinant proteins were initially evaluated by activating grouper FSH receptor, and further demonstrated by incubating ovarian fragments of adult grouper and intraperitoneal injection in juvenile female grouper. Two forms of recombinant FSH presented similar biological activities of activating FSH receptor and stimulating in vitro testosterone (T) and estradiol-17β (E2) secretion, though the dimer form functioned slightly weaker than the single-chain form. However, injections of rgFSHb-a or rgFSHba could significantly increase serum T and E2 levels, induce early ovarian development, reduce hypothalamic gnrh1 mRNA level, and increase hypothalamic cyp19a1b mRNA level. Data in this study suggested that recombinant gonadotropin could be produced in dimer form or single-chain form by P. pastoris, and FSH could regulate steroidogenesis and early ovarian development in juvenile grouper.

Expression of recombinant zebrafish follicle-stimulating hormone (FSH) in methylotropic yeast Pichia pastoris

Pituitary gonadotropin follicle-stimulating hormone (FSH) was identified in fish two decades ago, but its functional importance in fish reproduction remains poorly defined, especially in non-salmonid species. This gap in our knowledge is partially due to the lack of the hormone in pure form in most of the species studied. We describe here the production of two different forms of biologically active recombinant zebrafish FSH (zfFSH and zfFSH(HIS)) using methylotrophic yeast, Pichia pastoris, as the bioreactor. One form (zfFSH) was produced as the molecule closer to the native form, with the two subunits (Cga and Fshb) expressed separately under different promoters. The other form (zfFSH(HIS)) was produced as a single polypeptide, with the cDNAs for the two subunits joined to form a fusion gene that contained a 6X His tag as part of the linker between the two subunits. The culture conditions were optimized for pH and incubation time for maximal production of the proteins. Using a zebrafish FSH receptor (Fshr)-based reporter gene assay, we tested and compared the biological activities of the two forms of recombinant zebrafish FSH. Our results provide useful information for the future production of recombinant gonadotropins in other fish species.

Synthesis and characterization of biologically active recombinant elk and horse FSH

The objective of this investigation was to clone and express the elk and horse common alpha-subunit and FSH beta-subunit cDNAs, and to produce recombinant FSH from both species in vitro. The RNAs extracted from elk and horse pituitary glands were reverse-transcribed and amplified by polymerase chain reaction. The cDNAs corresponding to both subunits of elk and horse were cloned into the expression vector pBudCE4.1 and transfected into CRL-9096 cells. Expression of both genes was determined in the transfected cells by Northern and Western blot analysis. Recombinant elk and horse FSH secreted in culture media were characterized by an in vitro bioassay and RIA. When the recombinant products were assessed as activity over mass of FSH measured by RIA, the horse product was 5.6 times more potent than the elk product. The recombinant products injected to immature female Wistar rats stimulated ovarian growth. The results suggest that the products obtained correspond to recombinant versions of the native elk and horse FSH. The availability of these recombinant products may aid in the development of more predictable and efficient techniques of ovarian stimulation in cervids, equids, and other species as well.

Co-expression of human protein disulfide isomerase (hPDI) enhances secretion of bovine follicle-stimulating hormone (bFSH) in Pichia pastoris

Bovine follicle-stimulating hormone (bFSH) is a pituitary gonadotropin composed of two non-covalently associated polypeptide subunits, which must be glycosylated, folded, and assembled as a heterodimer to be biologically active. Low-level expression of the recombinant bFSH is the factor that limits its usefulness as a superovulation treatment for cows. To increase the production of recombinant bFSH, human protein disulfide isomerase (hPDI) was expressed simultaneously in engineered Pichia strains. The secretion characteristics of bFSH with or without hPDI were examined. The co-expression of bFSH and hPDI is increased to 1.56 mg/l of heterodimer in the culture medium, which is 6-fold higher when compared with the control strain carrying the bFSH gene only. These results may be generally applicable to increase the expression of other glycoprotein hormones in yeast.

Tilapia Follicle-Stimulating Hormone (FSH): Immunochemistry, Stimulation by Gonadotropin-Releasing Hormone, and Effect of Biologically Active Recombinant FSH on Steroid Secretion1

In fish, FSH is generally important for early gonadal development and vitellogenesis. As in mammals, FSH is a heterodimer composed of an alpha subunit that is noncovalently associated with the hormone-specific beta subunit. The objective of the present study was to express glycosylated, properly folded, and biologically active tilapia FSH (tFSH) using the Pichia pastoris expression system. Using this material, we aimed to develop a specific ELISA and to enable the study of FSH response to GnRH. The methylotrophic yeast P. pastoris was used to coexpress recombinant genes formed by fusion of mating factor alpha leader and tilapia fshb and cga coding sequences. Western blot analysis of tilapia pituitary FSH, resolved by SDS-PAGE, yielded a band of 15 kDa, while recombinant tFSH beta (rtFSH beta) and rtFSH beta alpha had molecular masses of 17-18 kDa and 26-30 kDa, respectively. Recombinant tFSH beta alpha was found to bear only N-linked carbohydrates. Recombinant tFSH beta alpha significantly enhanced 11-ketotestosterone (11-KT) and estradiol secretion from tilapia testes and ovaries, respectively, in a dose-dependent manner (similar to tilapia pituitary extract, affinity-purified pituitary FSH, and porcine FSH). Using antibodies raised against rtFSH beta, FSH-containing cells were localized adjacent to hypothalamic nerve fibers ramifying in the proximal pars distalis (PPD), while LH cells were localized in a more peripheral region of the PPD. Moreover, FSH is under the control of hypothalamic decapeptide GnRH, an effect that was abolished through the use of specific bioneutralizing antisera, anti-rtFSH beta. It also reduced basal secretion of 11-KT.

Expression of a recombinant anticoagulant C-type lectin-like protein ACFI in Pichia pastoris: heterodimerization of two subunits is required for its function

ACFI is an anticoagulant C-type lectin-like protein (CLP) isolated from Agkistrodon acutus venom. To investigate the function of ACFI and its subunits, the cDNAs of two subunits were transformed and expressed in Pichia pastoris separately or together by a novel strategy using two vectors with different selectable markers. The results showed that recombinant homodimers were secreted when the subunits were expressed alone, while heterodimers (rACFI) were secreted when two subunits were co-expressed. The secreted proteins were purified from culture supernatants in one step by metal-chelating affinity chromatography with the yields of 1-4 mg/L. PAGE and ELISA showed that rACFI competed the binding of native ACFI for human factor X and IX with affinities of 1.6 and 30 nM, respectively. In addition, rACFI prolonged the activated partial thromboplastin time (APTT) in a concentration dependent manner as same as native ACFI. However, recombinant alpha or beta homodimers completely lost these activities, indicating the heterodimerization of two subunits is required for its function. It also suggests that P. pastoris is a promising system for structure-function studies of snake CLPs.

Heterologous expression of piglet odorant-binding protein in Pichia pastoris: a comparative structural and functional characterization with native forms

This study targets to express the piglet odorant-binding protein (plOBP) and compare the engineered product to the corresponding native protein forms, i.e. plOBP and adult porcine OBP (pOBP). Using the natural signal peptide from the cDNA sequence, up to 40 mg l(-1) of secreted recombinant piglet OBP (rOBP) has been produced in a minimal culture medium. No significant difference in molecular mass between rOBP and native plOBP could be observed by mass spectrometry following or not trypsin digestion. rOBP and pOBP shared similar immunoreactivity towards polyclonal anti-pOBP antibodies, suggesting a proper processing and folding of the recombinant product. Both plOBP and rOBP displayed comparable binding properties towards fatty acids present in the putative maternal pheromone and a steroid, component of the boar sex pheromone. Furthermore, the rOBP product was found to bind to an olfactory receptor, for which pOBP binding was previously characterized. Taken together, these findings suggest that rOBP, produced in Pichia pastoris, exhibits structural and functional properties comparable to those of the native lipocalins from both young or adult animal.

Production of biologically active tethered tilapia LHbetaalpha by the methylotrophic yeast Pichia pastoris

In fish, luteinizing hormone (LH) stimulates processes leading to final oocyte maturation and ovulation in females, and spermiation in males. The hormone is a heterodimeric glycoprotein composed of two non-covalently associated subunits. In this study, we describe the expression of tilapia LH (tLH) as a biologically active, single-chain polypeptide using the methylotrophic yeast Pichia pastoris. The tLHbeta and alpha mature protein-coding sequences were joined to form a fusion gene that encodes a "tethered" polypeptide in which the tLHbeta-chain forms the N-terminal part and the alpha-chain forms the C-terminal part. A "linker" sequence of six amino acids (three Gly-Ser pairs) was placed between the beta- and alpha-chains to assist in the chimerization of the subunits, and a six-His tail was placed at the end of the beta-subunit, to enable purification of the recombinant protein. Western blot analysis of the pituitary LH resolved by SDS-PAGE yielded a band of 35 kDa, while the recombinant tLHbetaalpha had a molecular mass of 45 kDa, and was found to possess only N-linked carbohydrates. Recombinant tLHbetaalpha stimulated the release of 11-ketotestosterone from mature testes, whereas its release from immature testes was less pronounced.

Hyperexpression and purification of biologically active human luteinizing hormone and human chorionic gonadotropin using the methylotropic yeast, Pichia pastoris

The glycoprotein hormones, luteinizing hormone (LH), human chorionic gonadotropin (hCG), thyroid stimulating hormone (TSH), and follicle stimulating hormone (FSH), play important roles in overall physiology and reproduction. These hormones are heterodimeric molecules consisting of an identical alpha subunit non-covalently associated with the hormone-specific beta subunit. The inherent structural intricacies possessed by these hormones make them very interesting model systems for structure-function relationship studies of complex dimeric glycoproteins. The structural studies, as well as, the therapeutic applications require large quantities of biologically active hormones free of any contaminants. In this study, we report hyperexpression and purification of biologically active recombinant hLH and hCG expressed using Pichia pastoris expression system. A combination of hydrophobic interaction chromatography and ion exchange chromatography has been used to purify these recombinant hormones to homogeneity. Using a number of biochemical and immunological criteria, the recombinant hormones have been shown to be similar to the natural hormones and were equally biologically active. The preliminary data also suggested that P. pastoris cells express a low molecular weight isoform of hCG that appeared to be less glycosylated. This isoform exhibited lesser affinity for the receptor as compared to hCG, but was found to be fully biologically active.

Expression of a biologically active recombinant follicle stimulating hormone of Japanese Eel Anguilla japonica using methylotropic yeast, Pichia pastoris

In the Japanese eel Anguilla japonica, the administration of exogenous GTH is necessary for the artificial induction and completion of gonadal maturation due to its GTH deficiency under captive conditions. The isolation of native eel GTH has not been accomplished, which has made it difficult to fully elucidate the biological functioning of the two GTHs (FSH and LH) in eel. In this study, we attempted to produce a recombinant Japanese eel GTH (rjeFSH) having biological activity using methylotrophic yeast, Pichia pastoris in order to gain more understanding of the functioning of GTH in this species. An expression vector in which jeFSHbeta and GTHalpha subunit cDNAs were tandemly connected was constructed. P. pastoris was transformed with the vector, and rjeFSH was expressed. The rjeFSH thus expressed was detected by Western blot analysis. The glycoprotein fraction of the yeast culture supernatant was separated by native PAGE, and a band showed positive reaction with anti-GTHalpha and FSHbeta antisera similarly, suggesting that both subunits are associated. After deglycosylation, both subunits were decreased in molecular mass, indicating that rjeFSH was glycosylated. In in vitro assay, rjeFSH stimulated the release of testosterone and 11-ketotestosterone from immature eel testis, whereas release was not stimulated in maturing eel testis. This is the first report investigating the biological activity of eel GTH using the recombinant eel FSH.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

Expression of a single betaalpha chain protein of equine LH/CG in milk of transgenic rabbits and its biological activity

Equine chorionic gonadotropin (eCG) is a heavily glycosylated glycoprotein composed of non-covalently linked alpha- and beta-subunits. eCG possesses the particularity to bind to both LH and FSH receptors in species other than horses and to have a prolonged plasma half-life. All these properties make it of utmost interest for livestock fertilization program. Up to now, the only source of eCG is the serum of pregnant mare. Rabbit mammary gland is considered as a system able to produce recombinant glycoproteins in sufficient quantity for pharmaceutical use. Here we described the production of a recombinant single betaalpha chain of eLH/CG in the milk of transgenic rabbit. The construction of a single-chain permits to by-pass the problem of association-dissociation of the subunits. This recombinant hormone is greatly expressed (21.7 mg/l) and presents similar in vitro LH and FSH bioactivities. However, betaalphaeLH/CG shows an extremely rapid clearance (approximately 10 min), which could explain the absence of in vivo biological activity. So the rabbit mammary gland is not appropriate for the production of a recombinant active eLH/CG.

Recombinant protein expression in Pichia pastoris

The methylotrophic yeast Pichia pastoris is now one of the standard tools used in molecular biology for the generation of recombinant protein. P. pastoris has demonstrated its most powerful success as a large-scale (fermentation) recombinant protein production tool. What began more than 20 years ago as a program to convert abundant methanol to a protein source for animal feed has been developed into what is today two important biological tools: a model eukaryote used in cell biology research and a recombinant protein production system. To date well over 200 heterologous proteins have been expressed in P. pastoris. Significant advances in the development of new strains and vectors, improved techniques, and the commercial availability of these tools coupled with a better understanding of the biology of Pichia species have led to this microbe's value and power in commercial and research labs alike.

Molecular architecture and biorecognition processes of the cystine knot protein superfamily: part I. The glycoprotein hormones

In this review article, the reader is introduced to recent advances in our knowledge on a subset of the cystine knot superfamily of homo- and hetero-dimeric proteins, from the perspective of the endocrine glycoprotein hormone family of proteins: follitropin (FSH), Iutropin (LH), thyrotropin. (TSH) and chorionic gonadotropin (CG). Subsequent papers will address the structure-function behaviour of other members of this increasingly significant family of proteins, including various members of the transforming growth factor-beta (TGF-beta) family of proteins, the activins, inhibins, bone morphogenic growth factor, platelet derived growth factor-beta, nerve growth factor and more than 35 other proteins with similar topological features. In the present review article, specific emphasis has been placed on advances with the glycoprotein hormones (GPHs) that have facilitated greater insight into their physiological functions, molecular structures and most importantly the basis of the molecular recognition events that lead to the formation of hetero-dimeric structures as well as their specific and selective recognition by their corresponding receptors and antibodies. Thus, this review article focuses on the structural motifs involved in receptor recognition and the current techniques available to identify these regions, including the role of immunological methodology, peptide fragment design and synthesis and mutagenesis to delineate their structure-function relationships and molecular recognition behaviour.

Single-step purification of recombinant human growth hormone (hGH) directly from bacterial osmotic shock fluids, for the purpose of (125)I-hGH preparation

A good quality tracer, to be used in the radioimmunoassay of human growth hormone, was prepared by applying the chloramine-T iodination technique to the recombinant product obtained after a single-step high-performance size-exclusion chromatography purification of a bacterial osmotic shock fluid. The labeling reaction presented a yield of about 65% and the purified tracer exhibited an antibody binding of approximately 50% (NIDDK reference antiserum diluted 1:600,000). These values are very similar to those obtained by radioiodinating highly purified clinical-grade recombinant human growth hormone obtained from the same periplasmic extract after the regular six-step purification process. Both tracers provided the same accuracy, when evaluated with the use of commercial-quality control samples in a classical radioimmunoassay methodology, their stability being practically identical: about 18% decrease in antibody binding after 2 months of storage at -20 degrees C. The novel approach permits the utilization of transformed Escherichia coli strains as a source of freshly prepared, radioiodination-grade recombinant proteins, capable of providing better reproducibility and reagent continuity.

Heterologous protein expression in the methylotrophic yeast Pichia pastoris

During the past 15 years, the methylotrophic yeast Pichia pastoris has developed into a highly successful system for the production of a variety of heterologous proteins. The increasing popularity of this particular expression system can be attributed to several factors, most importantly: (1) the simplicity of techniques needed for the molecular genetic manipulation of P. pastoris and their similarity to those of Saccharomyces cerevisiae, one of the most well-characterized experimental systems in modern biology; (2) the ability of P. pastoris to produce foreign proteins at high levels, either intracellularly or extracellularly; (3) the capability of performing many eukaryotic post-translational modifications, such as glycosylation, disulfide bond formation and proteolytic processing; and (4) the availability of the expression system as a commercially available kit. In this paper, we review the P. pastoris expression system: how it was developed, how it works, and what proteins have been produced. We also describe new promoters and auxotrophic marker/host strain combinations which extend the usefulness of the system.